1. Field of the Invention
The present invention relates to a cooling system for an electronic circuit device. More particularly, it relates to a printed circuit board holding electronic circuit components, such as semiconductors, large scale integrated circuits (LSI's), or integrated circuit (IC's), wherein these components are cooled by a cooling system that includes a cooling module or a series of cooling modules for removing the heat dissipated from the component and transferring it to a coolant flowing in a passage.
2. Description of the Related Art
In conventional cooling modules for electronic circuit devices, a heat transfer element such as a heat transfer plate or a heat sink head is pushed against the circuit components, such as IC's, LSI's, and semiconductors, by pressure from a spring or a bellows, to remove the heat dissipated from these circuit components. The heat transfer elements are exposed to a coolant (usually a gaseous coolant), in such a manner that the heat removed from the circuit components is transferred to the coolant by the corresponding heat transfer element.
Located between the heat transfer plate and the circuit component is a deformable or elastic thermal conductive sheet, such as a thermal sheet, and a second heat transfer plate can be located between the thermal sheet and the circuit component to be cooled. The thermal sheet usually consists of, for example, a silicone-containing material such as silicone rubber having incorporated therein a metal or metal oxide, such as alumina, beryllia to increase thermal conductivity and to bind the plastic material. The heat transfer between the first heat transfer plate and the corresponding circuit component is effected through the thermal sheet (and the second heat transfer plates, if any).
Since, however, the thermal sheet is made of a soft plastic material as a matrix material, although metal powders having a high heat conductivity are mixed therein, the heat conductivity is still relatively small. And it is generally not possible to increase the amount of the included metal component, as this will decrease the elasticity of the thermal sheet. Furthermore, since the thermal sheet is solid, although elastic, complete surface contact between the first heat transfer plate and the circuit component or between the first and second heat transfer plates can not be achieved if there is any unevenness or distortion in the contacting surfaces of the first or second heat transfer plate or the circuit component. Such incomplete surface contact results in large and non-uniform thermal transfer resistance, and any change in the pressure from the spring or bellows leads directly to a change in the thermal transfer resistance, resulting in unstable thermal transfer resistance. These factors decrease the heat transfer efficiency.